<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>
.pad { padding: 100%; }
</style>
</head>

<body>

    <table>
      <div class="pad">x</div>
      <tr>
        <td>a</td>
        <td>b</td>
        <div class="pad">c</div>
      </tr>
    </table> 

</body>

</html>
